1. Field of the Invention
This invention relates to electrical connectors affixed to printed circuit boards and, more particularly, to providing retaining means for such connectors while its terminal pins are soldered to the printed curcuit board.
2. Description of Related Art
Since the advent of the printed circuit board, electrical components have generally been affixed to the board by soldering the component leads to the printed electrical pattern. Often times the component leads extend through the board's holes and must be soldered in this position.
One of the problems encountered in such operations is maintaining the components in the desired position or orientation during assembly and soldering. Various attempts have been made to solve this problem. In earlier times when discrete electrical components such as capacitors and resistors were commonly affixed in large numbers to printed circuit boards, various lead locking arrangements were suggested. For example, in U.S. Pat. No. 2,754,486 granted July 10, 1956 to C. J. Hathorn, the two relatively soft lead wires of a resistor were twisted in a configuration so when inserted, the leads temporarily lock by hooking around the side and edge of the board holes, to thereby hold the resistor in place while soldering. Similar approaches were proposed for capacitors in U.S. Pat. No. 3,162,721, granted Dec. 22, 1964, U.S. Pat. No. 3,056,939 granted Oct. 2, 1962, and U.S. Pat. No. 3,239,720 granted Mar. 8, 1962, all to C. C. Rayburn, as well as U.S. Pat. No. 3,747,045 granted July 17, 1973 to H. A. Stross. Where such discrete components have been packaged together, similar techniques have been tried. U.S. Pat. No. 3,524,108 granted Aug. 11, 1970 to J. A. English, for example, discloses a board mounted modular circuit component comprising a hard dielectric ceramic material supporting a number of active and passive components with multiple, self-locking leads bent into a configuration so as to provide cam surfaces for contacting the printed circuit board holes.
Retention during soldering is particularly important in connection with the more recent multi-terminal connectors. Where such connectors have flat, thin leads, which can be readily crimped as in the discrete components of the past, the retention is not a serious problem. This is because the easily crimped flat, thin leads usually have a large offset permitting adequate room to pass through the board holes. The crimped portion passes completely through holes and locks to the other end of the holes. To provide adequate retention, the thickness of the board and location are critical.
In the case of electrical connector headers, lead locking arrangements of the prior art are not easily applied. Such headers include numerous male terminal pins surrounded by various plastics. The male pins are typically square metal posts approximately 0.025 inches square and are very stiff. Because of the size and stiffness of such square male pins, headers are soldered to printed circuit utilizing various hold-down devices to retain the header in place during the soldering operation. Such devices include mechanical fasteners such as bolts and screws. Weighted plates are also used. These are placed atop the headers and removed after the soldering process. Although such methods work, they are expensive because they are labor intensive.
Within the last few years, methods of attachment which are an integral part of the header have been sought. What has been tried typically involves employing a single male pin in the header which will interfere with one printed circuit board hole. The male pin used is commonly one of the commercially available compliant-type pins. Such pins, however, usually require high insertion forces on the order of 40 pounds. Also, they are useful for one insertion only.
The move to robotic insertion has lead to a need for a header that can be mechanically placed on a printed circuit board and automatically retained through subsequent board handling and soldering operations. Robotic loaders typically have an upper limit on insertion forces (for example, about 15 pounds) to protect the circuit board in case of a misplaced or damaged component. As this load limit is reached, the insertion head of the robotic loader retracts to provide this safety feature. Consequently, retention features must have relatively low insertion forces to be used with robotic loaders.